A 40-GHz-bandwidth, 4-bit, time-interleaved A/D converter using photoconductive sampling |
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Authors: | Nathawad L.Y. Urata R. Wooley B.A. Miller D.A.B. |
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Affiliation: | Center for Integrated Syst., Stanford Univ., CA, USA; |
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Abstract: | GaAs photoconductive switches have been integrated with two parallel 4-bit CMOS analog-to-digital (A/D) converter channels to demonstrate the time-interleaved sampling of wideband signals. The picosecond sampling aperture provided by low-temperature-grown-GaAs metal-semiconductor-metal switches, in combination with low-jitter short-pulse lasers, enables the optically-triggered sampling of electrical signals with tens of gigahertz bandwidth at low to medium resolution. A pair of parallel sampling paths, one for sampling and the second for feedthrough cancellation, generate a differential held signal that is quantized by a low-input capacitance, high-speed flash A/D converter. Dynamic offset averaging is employed to improve converter linearity. An experimental time-interleaved two-channel A/D converter provides about 3.5 effective bits of resolution for inputs up to 40 GHz when tested at an optically-triggered sampling rate of 160 MHz. The sampling rate was limited by the available optical source. Each A/D converter channel operates up to a 640-MHz conversion rate, dissipates 70 mW of power, and occupies an area of 150 /spl mu/m /spl times/ 450 /spl mu/m in a 2.5-V, 0.25-/spl mu/m CMOS technology. |
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